Conventionally, inkjet recording devices are known as recording devices capable of printing on various recording mediums, including a typical example of plain paper. An inkjet recording device forms an image on a recording medium by directly jetting inks, which are coloring materials, onto the recording medium from nozzles arranged at the surface of recording heads facing the recording medium to make the inks land on the recording medium and infiltrate into or fix on the recording medium. Such an inkjet recording device has excellent features of simplicity of process, quietness during printing, and the quality of printing characters and images.
Such an inkjet recording device generally performs printing by the use of process color inks in colors of cyan, magenta, yellow, and black. In recent years, for special printing, attempts have been made to develop a method of improving the added value of an obtained image by superimposingly printing in special colors in addition to process colors.
For example, an image forming method is known that performs printing with white ink on a transparent base material, such as a soft wrapping material or film. This image forming method performs back printing in process colors on a transparent base material and thereafter superimposingly jets white ink on the printed surface. In such a manner, the printed image is observed as a right view when viewed from the side opposite to the side to which the white ink is adhering, in other words, when viewed from the transparent base material side. Further, an effect is obtained that prevents unclear recognition of an image caused by color transparency due to the transparent base material. This printing b the use of white ink in such a manner is called back printing, since the printing is performed on the side of the base material opposite to the side from which a view is taken.
On the other hand, in the case of using a colored base material, an image printed on the base material may be affected by the color of the base material, which may inhibit recognition of a right color of the image. In such a case, printing is performed on the surface of the basic material with white ink first, and then an image is superimposedly printed with process color ink on the surface of the print of the white ink. Herein, printing by the use of white ink in such a manner is called ‘front printing’ because printing is performed on the side, of the base material, from which a view is taken.
Inkjet recording devices have been developed which employ an image forming method that uses inks for forming real images, such process color inks as described above, and uses also a non-process color ink as a background color, such as white ink (refer to Patent Documents 1 to 3).                (Patent Document 1) Japanese Unexamined Patent Publication TOKKAI No. 2003-285422        (Patent Document 2) Japanese Unexamined Patent Publication TOKKAI No. 2004-306591        (Patent Document 3) Japanese Unexamined Patent Publication TOKKAI No. 2005-59214        
In such an inkjet recording device, recording heads (background recording heads) for jetting background recording ink are disposed at positions between which recording heads (heads) for jetting real image recording ink are disposed.
In a device disclosed in Patent Document 1, for front printing, a background recording head is disposed at a position forward from image recording heads with respect to the moving direction of the carriage, and for back printing, a background recording head is disposed at a position behind the image recording heads with respect to the moving direction of the carriage. Accordingly, in the case of performing both front printing and back printing, background recording heads are necessary on the both sides of image recording heads. In Patent Document 2, also disclosed is a device, as an example, that performs front printing with a background recording head disposed on the downstream side of image recording heads with respect to the conveying direction of a base material, and performs back printing with a background recording head disposed on the upstream side of image recording heads.
In any case where background recording heads are arranged such that image recording heads are disposed between the background recording heads along the carriage moving direction, the number of background recording heads increases and the size of the carriage becomes larger. Herein, the device disclosed in Patent Document 3 has a structure that instantly cures ink just after the ink is jetted from a background recording head so as to prevent mixing of the background recording ink with image recording ink, wherein background recording ink is cured with UV-light after being jetted from the background recording head and landing on a base material. However, such a structure further increases the size of the carriage.
Particularly, in a structure where background recording heads are disposed on the upstream and downstream sides along the direction of conveying a recording medium, the area, for printing on a base material, of the platen surface becomes large to cause a problem of lowering the conveying accuracy.
Further, in a case where ink is cured by irradiation from a UV-light irradiating device, since the arc length of the UV-light irradiating device becomes large, another problem is caused by heat development.
In this situation, in order to avoid mounting plural background recording heads on a carriage, a device has been developed in which a background recording head is mounted only on one side of image recording heads. In the case of performing front printing by this device, a background image is printed during forward motion of the carriage, and a real image is printed, during backward motion of the carriage, on the base material on which the background image has been printed.
However, even with this device, image deviation may be caused between a background image and real image, depending on the conveying accuracy.
As described above, there have been cases where high-definition recording images cannot be obtained by mounting a background recording head/heads on a carriage in addition to image recording heads.
In this situation, an object of the invention is to provide an inkjet recording apparatus that prevents lowering of conveying accuracy and prevents image deviation caused by an increase in the size of a carriage and thus achieves a high-definition image, even a background recording head is mounted on the carriage.